Scrap melters have been developed that are particularly intended for remelting light gauge scrap such as metal chips from a machine shop, or for used beverage cans. Such scrap has the property of being difficult to incorporate into a molten metal pool. Air may be trapped in the scrap, or an oxide layer on the scrap, contacting an oxide layer on the molten metal pool, may prevent the metal in the scrap from contacting the metal in the pool. It is particularly true of aluminum that the oxide layer is very strong and hard to break. If one heats light gauge aluminum scrap above the melting point of aluminum, one is likely to obtain piles of aluminum oxide containing molten aluminum, rather than a pool of molten aluminum.
Various prior art systems have employed vigorous movement of liquid metal, which serves to break oxide films and incorporate light gauge scrap into a pool or stream of liquid metal.
U.S. Pat. No. 6,074,455 entitled “Aluminum Scrap Melting Process and Apparatus” teaches an apparatus that includes a furnace which supplies hot molten metal to a first melting bay through an opening in the bottom of the first melting bay. An impeller driven by a vertical shaft draws liquid metal upwardly, into the first melting bay, and imparts a rotary motion to the liquid metal to produce a vortex of molten metal. Scrap metal is supplied to the vortex, which ingests the scrap metal. The wall of the first melting bay has a spiral form defining an exit channel which leads to an adjacent melting bay. The rotary motion of the liquid metal causes it to flow out of the exit channel and into the adjacent melting bay, where skim is removed. Molten salt in that bay may facilitate the separation of aluminum from the skim. Alternatively, salt may be added in a fluxing bay disposed at the output of the exit channel, between the first melting bay and the second melting bay. Molten salt tends to separate the molten aluminum from the oxide layer on the aluminum.
U.S. Pat. No. 5,930,986 “Apparatus for Immersing Solids Into Fluids and Moving Fluids in a Linear Direction” teaches an impeller assembly including an impeller which is surrounded by a hollow cylindrical portion that is attached to the impeller blades. The cylindrical portion may extend axially in either direction, upstream or downstream of the impeller blades. The impeller is shown mounted with a vertical shaft, and floating solids being drawn downward into the impeller, on the surface of a vortex created by the impeller.
U.S. Pat. No. 6,723,276 “Scrap Melter and Impeller” teaches an impeller without a cylindrical sleeve. The impeller is shown mounted on a vertical shaft. Blades of the impeller may or may not have pitch. In either case, a vortex is created, which serves to submerge scrap metal floating on the surface of the vortex.
U.S. Pat. No. 4,286,985 “Vortex Melting System” teaches an improved method and apparatus for ingesting and melting metal scrap that otherwise tends to float on the surface of a molten melting medium. A supply of molten metal is divided into two streams which flow into a receptacle. The receptacle has a submerged outlet. One of the streams enters the receptacle tangentially to produce a vortex. The other stream enters radially and it breaks up the symmetry of the vortex in a manner which enhances ingestion of floating scrap into the vortex.
FIGS. 1, 2 and 3 are schematic illustrations of a typical prior art system for melting scrap such as used aluminum beverage cans. Liquid metal is heated in a furnace and flows to a circulating pump, as seen in FIG. 1. It then flows into a receptacle resembling a toilet bowl where it forms a vortex. Scrap is supplied to the vortex, where it is ingested into the metal stream. It flows out of a submerged outlet into a skim bay, where oxides and other nonmetallic solids are skimmed off. It then flows back to the furnace.
FIG. 2 is an illustration of the prior art system illustrated in FIG. 1; FIG. 2 further defining section 3-3.
FIG. 3 refers to the prior art system illustrated in FIGS. 1 and 2. FIG. 3 is a vertical section cut along line 3-3 in FIG. 2. From the furnace on the left, the liquid metal flows to the pump bay where it is pumped into the charge bay, which was referred to as a “toilet bowl” in FIG. 1. The molten metal, with the melted scrap, flows downward to a submerged outlet and thence to the skim bay and thence back to the furnace.
There is a need in the art for a scrap metal melter that has fewer chambers and moving parts. There is also a need in the art for a scrap metal melter that minimizes oxidation of the metal and, hence, results in increased recycling efficiency.